I would love to see this. I would prefer this to be using an Adobe ID, but without subscription. Would be great if there is like a 2GB free tier (I believe there is for some Adobe products). If I share from my library to lets say my wife, the photos would be stored with me but she would still be able to add/edit/view/organize photos stored in my storage, using my storage limits.

With regards to co-editing photos with other people:

For this, I would really love to have virtual copies/snapshot functionality where both the owner and collaborator can do an edit and these can be compared. It would be great if the history would be more akin how it is in Luminar, where you can see each single action performed on a photo and can just step back in time (making it great to learn as well, since you can see how someone else achieved a look on a photo with which steps in the right order).

For this to work, it would be great to have commenting/annotation abilities as well which I will submit as a separate idea.

Collaborative features are one of the core benefits of the cloud which can never be matched/implemented in Lightroom Classic in the right way. I therefore believe this is one of the key areas where Lightroom CC will shine in the future... and a key selling point to get people to move from an old to a new paradigm (local vs cloud).

To summarize, I propose:

Google Docs style collaborative editing of photos (instead of documents) with some of the key features being: ownership rights and sharing, live editing with multiple people (great for classroom setting as well), annotation/commenting (annotation ON the image, commenting NEXT to the image in the sidebar) and version management (snapshots, so you can always go back through earlier states with an option to explicitly save specific Snapshots and name them, so you can easily switch between multiple edits of an image).

Annotation of images similar to iOS/Mac/Windows screenshoot tool, or Capture One where it is easy to draw on an image. This would also be super helpful during image review phase where you can quickly doodle on images to indicate problem areas.